The present invention relates to a method and apparatus for measuring vector magnetic flux. More particularly, the present invention relates to a method and apparatus for measuring vector magnetic flux based on magnetic flux components detected by corresponding pickup coils of plural magnetic flux meters which are disposed based on their predetermined relative positions, each magnetic flux meter including a body which has three faces crossing at right angles with respect to one another, and three pickup coils of corresponding superconducting quantum interference device magnetic flux meters including superconducting quantum interference devices (hereinafter referred to as SQUIDs) disposed on the corresponding faces of the body.
It is known that a SQUID is capable of detecting magnetic flux with extremely high sensitivity. To take notice of this characteristic, a SQUID is applied to various apparatus which are used in various technical fields. When magnetic fields of living organisms are to be measured, the magnetic flux at plural points present in a predetermined plane are measured by plural SQUID magnetic flux meters, then the magnetic flux at all points within the corresponding plane are calculated by performing linear interpolation, spline interpolation and the like based on the measured magnetic flux.
When not only the intensity of the magnetic flux but also the directions of the magnetic flux are to be taken into consideration, the magnetic flux at plural points are measured by plural vector magnetic flux meters, each vector magnetic flux meter including a mounting block 61 which has three faces 61a, 61b, 61c crossing at right angles, and three pickup coils 62a, 62b, 62c of a SQUID magnetic flux meter disposed on the corresponding faces of the mounting body 61 (refer to FIGS. 6(A), 6(B), and 6(C), then interpolation operations are carried out based on the measured vector magnetic flux. When it is supposed that the vector magnetic flux is measured accurately, the vector magnetic flux at all points within the corresponding plane is calculated accurately by performing interpolation operations based on the measured magnetic flux.
Vector magnetic flux obtained by vector magnetic flux meters actually includes an error, thereby calculated vector magnetic flux eventually includes an error. The cause of the errors is described in detail. The vector magnetic flux meter is used by positioning the pointed end 61d of the mounting block 61 closest to a measuring point and by supposing that obtained magnetic flux components in three directions are measured at a point 61e as a center of the vector magnetic flux meter. The point 61e is a center of gravity of a triangle which is defined by the centers 62d, 62e and 62f of the pickup coils 62a, 62b and 62c as apexes of the triangle (refer to FIG. 6(D) showing the triangle in broken lines). The centers 62d, 62e and 62f of the pickup coils 62a, 62b, 62c are actually apart from the center 61e of the vector magnetic flux meter by about 1 cm (refer to FIG. 6(B)), thereby magnetic flux components in corresponding directions are measured at different points with respect to one another. As a result, real vector magnetic flux at the center 61e of the vector magnetic flux meter cannot be measured. Furthermore, when the magnetic field is measured at plural points, plural vector magnetic flux meters are generally disposed at every distance of 2.5-4 cm causing the ratio of the distance between the center 61e of the vector magnetic flux meter and the center of the pickup coils to the disposition distance of the vector magnetic flux meters to increase to a value. Thereby, vector magnetic flux measurement error also is generated based on the increase of the ratio. Especially, when magnetic fields of living organisms are to be measured, the magnetic fields may have a fairly high gradient of spacial magnetic field. When the magnetic field has a fairly high gradient of spacial magnetic field, differences between measured magnetic flux components in corresponding directions and real magnetic flux components in corresponding directions, remarkably increase due to the distances between the center 61d of the vector magnetic flux meter and the centers of the pickup coils.
Diameters of the pickup coils may be decreased so as to decrease the distance between the pickup coils, to dissolve the disadvantages above-mentioned. A disadvantage arises in that the sensitivity of the vector magnetic flux meter is eventually lowered due to the decrease in the diameters of the pickup coils, thereby the signal to noise ratio is degraded.